This in invention relates to a stent for dilating and keeping open vessels and sealing-off aneurysms and inducing clotting in aneurysms, with a radially contracted stent for introduction into the vessel and with a radially expanded stent after introduction into the vessel.
Such stents or implantable catheters to be introduced into a body cavity, a vessel or the like can be made from plastic or an inert metal, such as steel or nickel-titanium alloys. Such stents are also referred to as endovascular or endoluminal stents or endoprostheses. For example, when dilating the ureter, the stents are used in the prostate region. In the case of benign prostate hyperplasia (BPH) or also in sclerotic blood vessels for dilating and keeping open the same. The stents have material areas and gaps between them. Thus, it is possible for the wall tissue of the organ kept open to grow round the stent. Stents can have a spiral construction, can be in the form of a helically wound coil or be in the form of a mesh fashioned from interconnected ribs. They can be made from woven or knitted wire or plastic material. Such stents can have memory properties, such as e.g. exist with certain nickel-titanium (nitinol).
A method of shaping a hollow tube after it has been placed in the body lumen is described by Unsworth and Waram in U.S. Pat. No. 5,846,247 (application Ser. No. 08/749,661 filed on Nov. 15, 1996), which patent is incorporated herein by specific reference. That patent describes a method of imparting virtually any shape on a shape memory alloy (SMA) tube, or a tube made of material having similar materials that exhibit shape recovery when heated to an appropriate temperature. That patent describes a device comprised of a side-firing laser or electrical probe that selectively heats parts of the inside of a tube of SMA material. By shape setting the tube to the desired shape at high temperature, then deforming the tube after it has cooled below the temperature at which it completely or nearly completely changes into its martensitic phase, one can create many shapes by heating part or parts of the tube to the temperature at which the selected parts of the material is transformed into its austenitic phase, thus recovering parts of the shape set into the tube at high temperature. That patent describes how a tube might be transformed into a coil stent it did not describe how a multiplicity of tubes might be formed into a mesh stent.
Any number of tubes can be arranged with their longitudinal axes parallel and their sides connected to each other at various places to form the walls of a larger tube. This larger tube can the be radially expanded by causing the smaller tubes to bend between the points of connection forming a webbed tubular structure. If the tubes are made of shape memory alloy (SMA) the larger webbed tube can be heat treated to its shape set temperature and when subsequently cooled below the martensitic finish temperature it can be radially formed into a more compact structure. After the shape setting and deformation steps, the expanded tubular structure can be recovered by heating it above the austenitic finish temperature. In its compact martensitic form, the webbed tube can be inserted into the lumen of a tubular body, then heated to support the walls forming the lumen.
The shape of the tubes forming the webbed tubular structure can each be recovered utilizing the method described by Unsworth and Waram in U.S. Pat. No. 5,846,247 (application Ser. No. 08/749,661 filed on Nov. 15, 1996), which patent is incorporated herein by specific reference. This method involves heating the SMA tubes with photo-thermal energy produced by a laser and delivered down an optical fiber. The photo-thermal energy is projected to the inside of the tubes at the distal end of the optical fiber by means of side-firing optics attached to the distal end of the fiber or incorporated into the distal end of the fiber. The area of projection can be varied depending upon the requirements of the particular application, by means of adjusting the optical side-firing means, means which are all well known to practitioners of the art.
As the optical fibers are withdrawn from the tubes, the optical fibers can apply photothermal energy to the inside of the tubes or while stationary in the tubes. Each fiber can be controlled individually, and depending upon whether or not the tube is heated and the shape is thereby recovered at a particular point, the shape of the entire webbed structure can be varied to best effect the purpose.
Short webbed tubular structures can be used in combination, being arranged end to end and being slidably attached only by the optical fibers that pass through their lumens. The optical fibers keep the sections of tubular structures aligned, but allow the train of sections to flex around curves in the body lumen. The flexibility of the train can be controlled by varying the ease with which the fibers slide within the lumens of the tube. By this means the train of webbed tubular structures can be made stiff or very flexible, depending upon the requirements of the case.
In lieu of optical fibers, wires or a probe containing wires and contacts, preferably flexible, can be used to deliver resistive heating to the SMA tube, or other conductive material, having suitable resistance, and exhibiting shape recovery properties when heated. This method is described in Unsworth and Waram in U.S. Pat. No. 5,846,247 (application Ser. No. 08/749,661 filed on Nov. 15, 1996).
It can be readily be seen that the stent fabricated from tubes as described, whether in one piece or a train of sections, offers the advantage of being able to vary the final shape of the stent by varying the parts of the webbed structure that are recovered. In the case of a train of sections, each can be deployed sequentially and separations between them can be controlled, either in advance, by their placement on the distal end of the catheter, or on the fly, by withdrawing the delivery catheter a desired distance, between deployments of the sections.
The fact that a balloon need not be used for deployment, although some preferred embodiments may include such a balloon, has the advantage of not impeding or stopping blood flow through the lumen into which it is placed, and deployed. While an important feature for stenting occlusions, it is especially important for aneurysms of the brain, where the inference with blood flow, for even a short time, can lead to serious brain damage. The controlled deployment of the stent and sealing means, also reduces trauma to the vessels into which the stent is deployed.
The method herein described allows for the stent to be covered with a membrane, which may be biodegradable, or other features that allow the stent to be impervious, or approximately impervious to blood or fluid flows through any openings in the walls of the stent. This features allows an aneurysm to be blocked off from the normal flow of blood or fluids, which travels through the lumen of the stent. By thus blocking off the aneurysm, clotting occurs in the aneurysm which causes it to form a plug that prevents further enlargement and rupture. A further advantage of stenting the vessel at and adjacent to the aneurysm, is that the aneurysm can be of any shape. Other methods, such as the placement of fibers or wires within the aneurysm to induce clotting, do not work if the opening in the vessel lumen is too large in relation to the size of the aneurysm bulb.
Further advantages and features of the invention can be gathered from the claims and description of a preferred embodiment of the invention with reference to the drawings.